Electrical winding of sheet conductor

ABSTRACT

A high-current capacity winding of sheet conductor for stationary induction apparatus which substantially reduces eddy current and circulating current losses has a plurality of coaxial coils each of which is spirally wound from a plurality of conductor sheets in parallel that extend the entire coil height with insulation between paralleled sheets and between spiral turns. Crossover connector strips extending parallel to the winding axis connect paralleled conductor sheets in the plurality of coils in series relation and so that the innermost and outermost of the paralleled conductor sheets of different coils are transposed and the net flux linkages of the plurality of flux paths are approximately equal.

United States Patent Waterman Feb. 22, 1972 [54] ELECTRICAL WINDING OFSHEET 3,464,043 8/1969 Benko et a1 ..336/185 X CONDUCTOR 3,466,5829/1969 Sealey et al. ..336/60 1,672,702 6/1928 Weed ..336/186 X [72]Inventor: Michael W. Waterman, Milwaukee, Wis.

Auk ha! M M and C Primary Examiner'l'homas .l. Kozma [73] Ass'gneeMilwfukemfiis' a g mummy Attorney-Lee H. Kaiser, Thomas F. Kirby andRobert B. Benson [22] Filed: Aug. 17, 1970 21 Appl. No.:- 64,472 [57]ABSTRACT A high-current capacity winding of sheet conductor for sta-[52] U S Cl 336/187 336/60 336/223 tionary induction apparatus whichsubstantially reduces eddy [51] 6 27/28 current and circulating currentlosses has a plurality of coaxial [58] Fieid 60 185 coils each of whichis spirally wound from a plurality of con- 6 ductor sheets in parallelthat extend the entire coil height with insulation between paralleledsheets and between spiral turns. Crossover connector strips extendingparallel to the winding [56] References cued axis connect paralleledconductor sheets in the plurality of UNITED STATES PATENTS coils inseries relation and so that the innermost and outermost of theparalleled conductor sheets of different coils are trans- 3,l95,0887/1965 Sandoz ..336/187 X posed and the net fl linkages f the pluralityf fl paths 2,436,207 2/1948 DEntremont.. .....336/186 x areapproximately equal, 2,998,583 8/1961 Worcester .336/223 X 3,546,64412/1970 Wilbum et al. ..336/187 2 Claims, 10 Drawing FiguresPAIENIEBrsazz I972 3. e44. 859

SHEET 2 BF 3 PATENTEUFEBZZ m2 3. 644, 859

saw 3 or a BACKGROUND OF THE INVENTION Shunt reactors may be used inhigh voltage, alternating current power transmission and distributionlines to compensate for line charging current and to allow the chargeremaining in the line to bleed to ground when the line is opened. Areactor is often immersed in oil within a tank, and the reactor may beconstructed without any magnetic material for a core so that it willhave high-magnetizing current. Such an air-core reactor sets up a largemagnetic field, and a problem with large size high voltage reactors isthat the magnetic flux near the ends of the reactor winding deviatesfrom the axial direction and has a cross direction relative to thewinding axis. This cross flux interacts with the current in theconductor turns of the windings to cause high eddy current losses and toproduce high axial compressive forces on the winding. Cross flux and itsdisadvantages are substantially eliminated in the extra high-voltage(EHV) shunt reactor disclosed in US. Pat. No. 3,362,000, in which I am ajoint inventor with William C. Sealey, wherein a closed magnetic yokehaving laminations in planes parallel to the axis of the reactor windingsurrounds the winding to reduce the reluctance of the magnetic circuitexternal to the winding to reduce the reluctance of the magnetic circuitexternal to the winding and has portions closely adjacent the axial endsof the winding to straighten the lines of magnetic flux within thewinding. The reactor winding is short in an axial direction andpreferably has a high ratio of winding radius to winding axial heightwhich further increases the inductance. The reactor winding disclosed insaid patent comprises a plurality of axially aligned pancake coilsdisposed in a stack and arranged in two similar groups of seriesconnected coils wound in opposite directions, and the patent disclosesthat the pancake coils may be wound from rectangular conductor having asubstantially wider dimension in the axial direction than in the radialdirection to improve the space factor. Reactors are also known whereinthe reactor winding is wound from a board ribbon of conductive materialwhich extends the entire axial height of the winding such as disclosedin U.S. Pat. No. 3,014,189 to McKinnon et a]. However, it has heretoforebeen impracticable to use such wide conductor ribbon in large kv./a.shunt reactor windings requiring conductor of large cross sectionbecause of the high eddy current losses which vary with the square ofthe dimension of the conductor at right angles to the direction of themagnetic flux.

It is an object of the invention to provide an improved high currentcapacity electrical winding for stationary induction apparatus which, incomparison to known structures, has reduced eddy current and circulatingcurrent losses, has a high space factor and increased short strength,and is simpler and less costly to manufacture.

BRIEF DESCRIPTION OF THE DRAWINGS This and other objects and advantagesof the invention will be more readily apparent from the followingdetailed description when considered in conjunction with theaccompanying drawing wherein:

FIG. 1 is a partial elevation view of a polyphase shunt reactor yoke andwinding assembly incorporating a preferred embodiment of the invention;

FIGS. 2 and 3 are views taken along lines II-II and III-III respectivelyof FIG. 1;

FIGS. 4 and 5 are enlarged partial views. of FIGS. 2 and 3 respectivelyshowing the crossover connectors;

FIG. 6 is a view taken along lines Vl-VI of FIG. 2;

' FIG. 7 and 8 are views similar to FIGS. 4 and 5 schematicallyillustrating alternative embodiments of the invention wherein a greaternumber of conductor sheets are wound in parallel than in the FIG. 1embodiment;

' FIG. 9 is an enlarged sectional view taken along line IX-IX of FIG. 2adjacent the abutting surfaces of the upper and lower coils; and

FIG. 10 is an enlarges sectional view taken along line X-X of FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENT Referring to the drawing, apolyphaseshunt reactor yoke and winding assembly incorporating a preferredembodiment of the invention has a plurality of cylindrical phasewindings A, B and C (of which only windings A and B are shown) arrangedwith their axes vertical and aligned in a common vertical plane. Thephase windings A, B and C are surrounded by a closed magnetic yoke 10which provides a low reluctance magnetic circuit external to thewindings. Yoke 10 has magnetic steel laminations 11 disposed in verticalplanes with upper and lower horizontal yoke portions 14 and 15respectively closely adjacent the axial ends of all phase windings A, Band C and connected by vertical end portions 16. The laminations llY ofthe upper and lower yoke portions 14 and 15 may have overlap miterjoints 17 with the laminations 11E of the end portions 16, and thenumber of laminations may vary in a horizontal direction in the mannerdisclosed in US. Pat. No. 3,466,582, in which I am a joint inventor withWilliam C. Sealey, so that the magnetic flux density is approximatelyuniform in any cross section through yoke 10.

The three phase windings A, B and C are identical, and only winding Awill be described. Winding A comprises an upper coil 20 wound fromsheet, or strip conductor such as aluminum as wide as the axial lengththereof and a lower coil 21 also wound from sheet, or strip conductorsuch as aluminum as wide as the axial length thereof. The upper andlower coils 20 and 21 are coaxial and connected in electrical seriesrelation and both are wound on the same insulating support tube 24 withan annular horizontal insulating washer 25 disposed therebetween. Washer25 may have apertures 30 therethrough (see FIG. 9) and radial insulatingspacers 31 art'- fixed to the upper surface thereof.

Upper coil 20 comprises inner and outer conductor sheets, or strips 22and 23 having a width substantially equal to the axial height of uppercoil 20 spirally wound counterclockwise in parallel. The large number ofspiral turns of strips 22 and 23 cannot be shown in FIGS. 2 and 3, andonly the inner turn and a portion of the outer turn are illustrated witha dotted line representation of the spiral convolutions connecting theinner and outer turns. Conductor sheets 22 and 23 may be covered with aninsulating film (not shown) such as epoxy resin or, alternatively, layerinsulation (not shown) of suitable material such as kraft paper sheetmay be wound between conductor sheets 22 and 23. Layer insulation 26(see FIG. 4) of suitable material such as sheet kraft paper is woundbetween the spiral multilayer turns of paralleled sheet conductors 22and 23.

Lower coil 21 similarly comprises inner and outer conductor sheets 28and 29 covered with an insulating film (not shown) and having a widthsubstantially equal to the axial height of lower coil 21 spirally woundclockwise in parallel with sheet layer insulation 26 between spiralmultilayer turns so that the direction of magnetic flux generated in theupper and lower coils 20 and 21 is the same. The conductor strips 22,23, 28 and 29 may be slightly narrower in an axial direction than thelayer insulation 26, and keepback insulation 35 may be disposed betweenwasher 25 and the edges of the strips 22 23, 28 and 29 to increase thedielectric breakdown strength between upper and lower coils 20 and 21.Elongated wooden spacer sticks 32 (see FIG. 9) extending parallel to thewinding axis are inserted at circumferentially spaced positions betweenthe spiral multilayer turns of the paralleled conductor sheets 22-23 ofthe upper coil 20 and also between spiral turns of paralleled conductorsheets 28-29 of lower coil 21 and form vertical ducts 33 for coolingfluid which extend through both the upper coil 20 and the lower coil 21and communicate with the horizontal ducts formed by the radial spacers31 and also with the apertures 30 in insulating washer 25.

The insulation film is removed from conductor sheets 22 and 23 at theoutward end thereof so that the outer ends of the sheet conductors 22and 23 are electrically connected together, and a START terminal 36 (seeFIGS. 1, 2 and 6) for winding A is provided on upper coil 20 and maycomprise a plurality of superimposed elongated strips 34 of conductivematerial such as aluminum welded to the outer ends of the conductorsheets 22 and 23 where they engage and are electrically connectedtogether. As shown in FIGS. 2 and 6, two elongated aluminum strips 34Aand 34B are disposed radially inward from the ends of the radially outerturn of the conductor sheets 22 and 23 and two elongated aluminum sheets34C and 34D are disposed radially outward from the conductor sheets 22and 23 adjacent the ends of the outer turn thereof, and the six layersof conductor 34A, 34B, 22, 23, 34C and 34D are welded together. Thesuperimposed elongated conductors 34A, 34B, 34C and 34D are bentoutwardly and upwardly adjacent the upper edge of the conductor sheets22 and 23 to form START terminal 36 for phase winding A of the shuntreactor. A horizontal phase bus bar 37 may be welded to the STARTterminal 36.

A FINISH terminal 38 for phase winding A of the shunt reactor isprovided adjacent the upper edge of lower coil 21 and is similar toSTART terminal 36. FINISH terminal 38 may be affixed to a horizontal busbar 40 which is electrically connected to similar FINISH terminals onthe other shunt reactor phase coils B and C to electrically connectphase coils A, B and C in wye. The insulation film is removed betweensheet conductors 28 and 29 at the ends of the outer turn thereof toelectrically connect these conductor sheets together at their outerends, and FINISH terminal 38 may comprise four elongated aluminum strips(not shown) welded to the outer ends of conductor sheets 28 and 29 wheresaid sheets abut in a manner similar to START terminal 36.

An annular insulating washer 44U having a plurality of apertures 46therethrough (see FIG. and elongated radial spacer members 45 affixed toboth surfaces thereof is positioned between the upper end of upper coil20 and the upper yoke portion 14 to form radial ducts in communicationwith the vertical ducts 33 and also with ducts 55 described hereinafterin coil 20, and a similar insulating washer 44L having apertures 46therein is positioned between the lower end of lower coil 21 and thelower horizontal yoke portion to form radial ducts communicating withthe vertical ducts 33 and 55 in lower coil 21.

Two elongated, straight, vertical aluminum crossover strip connectors 50and 51 electrically connect the inner and outer sheets 22 and 23 of thetop coil to the outer and inner sheets 29 and 28 respectively of thelower coil21, while keeping the two conducting paths insulated from eachother, to obtain the same netflex linkage for each conductor. Crossoverconnector 50 is disposed against outer sheet 23 of the upper coil 20along its entire vertical height and adjacent the inner end thereof (seeFIGS. 4 to 10) and is also disposed against the radially inner sheet 28of lower coil 21 along the entire vertical height thereof. Sheetinsulation 53 is folded in U- shape around the abutting crossoverconnector 50 and the end of outer conductor sheet 23 in upper coil 20,and the radially inner end 22i of inner conductor sheet 22 is bentaround such U-shaped insulation 53 and abuts against crossover connector51 along the entire vertical height of inner sheet 22.

In bottom coil 21 crossover connectors 50 and 51 abut against the radialouter surface of inner and outer sheets 28 and 29 respectively adjacentthe ends thereof. Sheet insulation 54, is folded in U-shape around theabutting portions of crossover connector 50 and inner sheet 28 in thelower coil 21 to isolate the two electrical paths. The inner conductorsheet 22 of top coil 20 is thus transposed so that it becomes the outerconductor sheet 29 of the lower coil 21, and also the outer conductorsheet 23 of top coil 20 is thus transposed so that it becomes the outerconductor sheet 28 of the lower coil 21. As described hereinbefore, thesheets 22 and 23 are electrically connected at their radial outer endsin upper coil 20, and the sheets 28 and 29 are electrically connected attheir radial outer ends in lower coil 21. The disclosed structure thusprovides a conductor having the same cross section but only one half thethickness of the conductor sheet of a reactor such as US. Pat. No.3,014,189 wherein the sheet conductor extends over the entire height ofthe reactor coil. It will be appreciated that such reduction inconductor thickness reduces to onefourth the eddy current losses (whichare proportional to the square of the conductor dimension perpendicularto the direction of magnetic flux). Further, inasmuch as the inner andouter conductor sheets are transposed so that they occur in differentradial positions in the upper and lower coils, the disclosed structureaverages out the fact that the self-inductance caused by the magneticflux is different in the inner and outer conductor sheets. Consequently,the circulating current generated by voltage inducted in the innerconductor sheet in one coil is canceled by the circulating currentgenerated by the voltage induced in the outer conductor sheet in theother coil.

As shown in FIGS. 4 and 5, cooling ducts 55 for an insulating fluid maybe provided between the support tube 24 and the first spiral multilayerturn of the paralleled conductor sheets, and the vertical elongatedwooden spacers 56 which form such ducts 55 and are in alignment with thecrossover connectors 50 and 51 are thinner in a radial direction thanthe vertical wooden spacers 57 which form such ducts 55 in the otherparts of the coil to prevent the crossover connectors 50 and 51 fromcausing a bulge in the coil. It will be appreciated that the radialthickness of such spacers 56 and 57 must be exaggerated in the drawing.Further, an elongated insulation pad 59 may be provided between thecrossover connector 51 and the first spiral turn of paralleled conductorsheets in both coils 20 and 21 to electrically isolate the two currentpaths.

FIG. 7 schematically illustrates an embodiment of the invention whereinthree conductor sheets 60, 61 and 62 are spirally wound in parallel inthe upper coil 20, similarly three conductor sheets 65, 66 and 67 arespirally wound in parallel in the lower coil 21, and three straightvertical crossover strip connectors 70, 71 and 72 electrically connectand transpose the sheet conductors so that the outermost sheet of thetop coil 20 is connected to the innermost sheet of the bottom coil bycrossover connector 70; the innermost sheet 62 of the top coil 20 isconnected to the outermost sheet 67 of the bottom coil 21 by crossoverconnector 72; and the center sheet 61 of top coil 20 is connected to thecenter sheet 66 of bottom coil 21 by crossover connector 71. Suchtransposition of the inner and outer sheets in the upper and lower coilsresults in substantially equal flux linkages for all three conductorsand in nearly total cancellation of circulating currents due to themagnetic flux. U-shaped insulating members schematically shown in dottedlines electrically isolate the three current paths at the positionswhere the crossover connectors 70, 71, and 72 connect coils 20 and 21 inseries. The folded portions at the inner ends of sheet conductors 61 and62 permit use of simple straight crossover connectors 70, 71 and 72which are easy to fabricate and connect to the conductor sheets andwithout causing bulges in the coils.

FIG. 8 schematically illustrates an embodiment similar to FIG. 7 whereinthree conductor sheets are spirally wound in parallel in both top coil20 and lower coil 21 but only one con ductor is transposed. Inner sheetconductor 62 of top coil 20 is bent in U-shape at its inner end so thatit abuts and is electrically connected to the upper end of crossoverstrip connector 72 which, at its lower end, abuts and is electricallyconnected to the outer sheet conductor 67 of lower coil 21. Thisconstruction results in substantial, but not perfect, cancellation ofthe circulating currents in the two coils 20 and 21 due to the magneticflux. The structure shown in FIG. 8 would result in equal net fluxlinkages for the three conductors and the total cancellation ofcirculating current if it were used to connect three coils in serieseach of which is spirally wound with three conductor sheets in parallel.

Although the invention has been illustrated and described as embodied ina shunt reactor winding, it will be appreciated that the invention isalso applicable to electrical windings for other stationary inductionapparatus such as power transformers.

It should thus be understood that I do not intend to be limited to theparticular embodiments shown and described, for many modifications andvariations will be obvious to those skilled in the art.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A shunt reactor winding having high-current capacity comprising, incombination,

a plurality of superimposed coaxial coils each of which is spirallywound from a plurality of conductor sheets in parallel terminatingtogether at their radially outer ends and which terminate at theirradially inner ends in a common radial plane and which sheets extendsubstantially the entire axial height of said coil, insulation betweenparalleled conductor sheets in each coil and between the spiral turns ofparalleled sheets,

a START terminal on one of said coils electrically connecting saidradially outer ends of the paralleled sheets of said one coil togetherand a FINISH tenninal on another of said coils electrically connectingsaid radially outer ends of the paralleled sheets of said another ofsaid coils together,

said plurality of coils being wound so that the direction of magneticflux is the same in all of said coils, and

means including a plurality of elongated flat crossover connector stripsdisposed in a common radial plane extending between adjacent coils atthe radially inner coil periphery in a direction parallel to the coilaxis and joining oppositely disposed radially inner conductor sheet endsin said adjacent coils for electrically connecting said paralleledsheets in said plurality of coils in series relation,

the radially inner ends of certain of said conductor sheets in one ofsaid adjacent coils being offset in a radial direction and joined tocrossover connector strips affixed to conductor sheets occupyingdifferent radial positions in said adjacent coil so that the net fluxlinkages of the plurality of conductor paths formed by said seriesconnected conductor sheets are approximately equal.

2. An electrical winding in accordance with claim 1 wherein the radiallyinner end of the radially inner conductor sheet in said one coil is bentin U-shape to a different radial position so that it is joined to aconductor strip afiixed to the radially inner end of the radially outerconductor sheet of said adjacent coil.

1. A shunt reactor winding having high-current capacity comprising, incombination, a plurality of superimposed coaxial coils each of which isspirally wound from a plurality of conductor sheets in parallelterminating together at their radially outer ends and which terminate attheir radially inner ends in a common radial plane and which sheetsextend substantially the entire axial height of said coil, insulationbetween paralleled conductor sheets in each coil and between the spiralturns of paralleled sheets, a START terminal on one of said coilselectrically connecting said radially outer ends of the paralleledsheets of said one coil together and a FINISH terminal on another ofsaid coils electrically connecting said radially outer ends of theparalleled sheets of said another of said coils together, said pluralityof coils being wound so that the direction of magnetic flux is the samein all of said coils, and means including a plurality of elongated flatcrossover connector strips disposed in a common radial plane extendingbetWeen adjacent coils at the radially inner coil periphery in adirection parallel to the coil axis and joining oppositely disposedradially inner conductor sheet ends in said adjacent coils forelectrically connecting said paralleled sheets in said plurality ofcoils in series relation, the radially inner ends of certain of saidconductor sheets in one of said adjacent coils being offset in a radialdirection and joined to crossover connector strips affixed to conductorsheets occupying different radial positions in said adjacent coil sothat the net flux linkages of the plurality of conductor paths formed bysaid series connected conductor sheets are approximately equal.
 2. Anelectrical winding in accordance with claim 1 wherein the radially innerend of the radially inner conductor sheet in said one coil is bent inU-shape to a different radial position so that it is joined to aconductor strip affixed to the radially inner end of the radially outerconductor sheet of said adjacent coil.